This invention relates to a digital frequency analyzer for frequency-analyzing various signals, such as a speech signal, into frequency components.
Frequency analyzers are widely used in vocoders and speech recognition systems. As illustrated by M. R. Schroeder in "Vocoders: Analysis and Synthesis of Speech", Proceedings of the IEEE, Vol. 54, No. 5 (May 1966), pages 720-734, with reference to FIG. 6 (Page 724), a conventional frequency analyzer comprises a predetermined number of analyzer channels each comprising a series connection of an analog band-pass filter of an individually preselected passband, an analog rectifier, and an analog low-pass filter of a commonly prescribed cutoff frequency. The number of channels is about ten or more in most cases so that use has to be made of ten or more band-pass filters, rectifiers, and low-pass filters each. The frequency analyzers have, therefore, been bulky and expensive. Above all, the low-pass filters must have a sufficiently large time constant in order to thoroughly remove ripples from the frequency components of the respective channels and have consequently been massive and costly.